Colon cancer develops through the stepwise accumulation of mutations. One of the earliest transforming mutations occurs in the K-RAS proto-oncogene. To develop effective anticancer agents, it is important to elucidate effectors of oncogenic K-RAS. Two known effectors of oncogenic K-RAS signaling are MEK/ERK and cellular redox pathways. Recently, oncogenic K-RAS was found to be closely associated with the overexpression of glutathione S-transferase pi1 (GSTP1) in colon cancer. The biological significance of this association remains unclear. GSTP1, a member of the glutathione S-transferase enzyme superfamily, is widely overexpressed in colon cancer. GSTP1 has known antioxidant, detoxification, and stress signaling functions. As such, there has been considerable clinical interest in GSTP1 as a tumor marker and as a therapeutic target. The preliminary data in this proposal demonstrate that the presence or absence of oncogenic KRAS determines cellular dependence on GSTP1. The mechanisms that underlie this observation are unknown. Recently, our lab reported that GSTP1 promotes MEK/ERK activation and protects against oxidative stress under growth-limiting conditions. These observations have led to the hypothesis that GSTP1 facilitates effective oncogenic K-RAS signaling by maintaining MEK/ERK activation and cellular redox. Three specific aims are proposed to test the above hypothesis: (1) To determine the mechanisms by which GSTP1 mediates oncogenic K-RAS activation of MEK and ERK, (2) To determine the mechanisms by which GSTP1 reduces oxidative stress generated by oncogenic K-RAS, and (3) To determine the role of GSTP1 in oncogenic K-RAS-promoted tumorigenicity in vivo. This proposal explores the paradox that while oncogenic K-RAS confers a mitogenic advantage to a cancer cell under growth-limiting conditions, it inadvertently renders the cell dependent on GSTP1. As such, a potential "Achilles Heel" may exist in colon cancers that harbor oncogenic K-RAS: they are more dependent on GSTP1 expression under growth-limiting conditions. This oncogenic dependence may eventually be exploitable for the therapy of colorectal cancer. [unreadable] [unreadable] [unreadable]